Polycarbonates are prepared on an industrial scale by the interfacial reaction of dihydroxy compounds with a carbonyl halide in the presence of a base. The majority of these processes are either batch processes, or xe2x80x9cbatch flowxe2x80x9d systems wherein all reactants other than gases are added to the reaction batch-wise, while gases are provided continuously throughout the reaction.
Present technology requires that every batch in the process be periodically sampled and analyzed to determine when satisfactory batch completion has taken place. This may be done by measuring the amount of free bisphenol present in the organic phase, or by determining the molecular weight of the polycarbonate resin product. The amount of free bisphenol may be quickly determined, but no acceptably fast analysis method is presently available to determine the molecular weight of the product. The lack of adequate testing methods results in loss of production time, excessive use of reagents to ensure that molecular weight build is complete, and exposure of personnel to low boiling point solvents.
Other methods have been developed to determine the completion of batch-wise polycarbonate reactions. U.S. Pat. No. 5,114,861 discloses a method for detecting the endpoint of an interfacial aromatic polycarbonate polymerization reaction comprising illuminating a sample of the polymerization reaction mixture with a light source and monitoring the extent of apparent light scattering of the sample throughout the course of the polycondensation reaction until, at the endpoint, a predetermined threshold extent of apparent light scattering is achieved. As with those previously described, this method requires periodic sampling, which results in loss of production time.
A method for determining the endpoint of an interfacial reaction between a dihydroxy compound and a carbonyl halide comprises determining the characteristic end point of the react on from a characteristic pH trace over time or ratio between caustic and carbonyl halide trace over time for the reaction; obtaining a pH trace over time or a ratio between caustic and carbonyl halide trace over time during the reaction to be monitored; and identifying the end point of he monitored reaction when the obtained pH or ratio trace resembles the end point determined from the characteristic pH or ratio trace.
The above described and other features are exemplified by the following figures and detailed description.